This invention generally relates to shuttleless weaving looms and more particularly to a mechanism for selecting a weft to be inserted into a shed of warps among a plurality of weft yarns with which is obtained a variegated weft pattern and feeding the selected weft to the weft insertion device by a predetermined length.
In general, the weft feeding mechanism is provided by two frictionally engageable rollers for each of plural weft yarns, one of which, referred to as a feed roller, is driven from any convenient loom shaft. The other, pressure roller is selectively brought into and out of pressure engagement with the feed roller by an appropriate weft selector means in accordance with weft pattern signals carried on a weft pattern card arrangement. In response to a weft pattern signal representing insertion of any weft, the corresponding pressure roller is pressed against the feed roller to grip the weft together with the feed roller, thus driving the measured length of the weft to a weft storage means, which weft is then fed to the weft insertion device. In the absence of this signal, the pressure roller is separated from the feed roller; the weft is released and remains still on the feed roller.
In this type of feed mechanism, rotation of the pressure roller is slowed down or stops in its inoperative position where it is separated from the feed roller. When the pressure roller is again brought into contact with the feed roller, there will thus be a relatively great peripheral speed difference between the two rollers. It follows that the weft yarn rubs against the outer surfaces of both rollers rotating at different speeds, resulting in breakage of thread or fray of filaments in case of a filament yarn. This of course objectionably influences the quality of a cloth woven in the loom with this mechanism.
Several proposals are so far made to avoid or alleviate this inconvenience in the weft feeding mechanism. One example is disclosed in U.S. Pat. No. 3,885,599 filed Oct. 1, 1973 under Ser. No. 402, 276 by Thomas Blackburn Mawdsley et al, in which the two shafts respectively carrying the rollers also carry thereon two pinions concentrically with the rollers. At the position of maximum separation of the rollers, the pinions remain in mesh with each other. In this prior art, accordingly, both rollers can be driven continuously whether supplying weft yarn or not to the storage element.
According to another known example, two pressure rollers are provided on a common shaft, one of which engages with the feed roller while the other is separated from the same. The pressure roller separated from the feed roller is positively driven from the other pressure roller in engagement with the feed roller via a drive transfer means in the form of a pair of rollers engaging respectively the pressure rollers. Thus the pressure roller in the inoperative position can be constantly rotated generally at the same peripheral speed as the pressure roller directly driven by the feed roller.
However, these two examples and others were found impractical for some reasons. For instance, in the first-mentioned example, the pressure roller is driven by the feed roller not directly but by way of the pinions also in its operative position engaging the feed roller. Hence, it is difficult to maintain exactly the same peripheral speed of the two rollers without highly precisely manufactured pinions and rollers. Wear of the rubber-coated outer surfaces of the rollers will accelerate the speed difference thus resulted between the two rollers. Also, an increased bulk and mounting space is taken, particularly in the latter example, for mounting the two pressure rollers and correspondingly two drive transfer rollers. Also the drive transfer member mounted above the pressure rollers will be a bar to handling the thread by the loom operator in the neighbourhood of the feed mechanism.